RESPONSES TO IRON-DEFICIENCY IN ARABIDOPSIS-THALIANA - THE TURBO IRONREDUCTASE DOES NOT DEPEND ON THE FORMATION OF ROOT HAIRS AND TRANSFERCELLS

Arabidopsis thaliana (L.) Heynh. Columbia wild type and a root hair-le ss mutant RM57 were grown on iron-containing and iron-deficient nutrie nt solutions. In both genotypes, ferric chelate reductase (FCR) of int act roots was induced upon iron deficiency and followed a Michaelis-Me nten kinetic with a K-m of 45 and 54 mu M Fe-III-EDTA and a V-max of 4 2 and 33 nmol Fe2+.(g FW)(-1).min(-1) for the wild type and the mutant , respectively. The pH optimum for the reaction was around pH 5.5. The approximately four fold stimulation of FCR activity was independent o f formation of root hairs and/or transfer cells induced by iron defici ency. Iron-deficiency-induced chlorosis and the development of a rigid root habit disappeared when ferric chelate was applied to the leaves, while FCR activity remained unchanged. The time course of the respons es to iron deficiency showed that morphological and physiological resp onses were controlled separately.